There has been substantial interest in recent years in maximizing the combined output powers from a plurality of solid state power sources, such as IMPATT and TRAPATT diodes mounted in a variety of power combining arrangements. Such interest has been stimulated in part by the increasing number of applications which require relatively lightweight and densely packed solid state power sources for generating high levels of microwave and millimeter wave power. For example, a signal transmitter on board a guided missile or a communications satellite has need for a high power solid state oscillators and amplifiers useful for the generation and amplification of microwave and millimeter wave energy, and solid state power combiner-type oscillators and amplifiers having the above-described characteristics are ideally suited for this purpose. Whereas traveling wave tubes (TWT's) have generally performed satisfactorily for this purpose in the past, there have nevertheless been continuing efforts to eliminate the dependence of the above electronic gear upon traveling wave tubes. Thus, there has been a trend to favor the all-solid-state type of power sources with their attendant advantages of increased reliability, lower cost, and their requirement for less space and weight in these high performance electronic applications.
Evidence of successful efforts in the development of microwave power combiners may be found in the widely copied IMPATT diode-type cylindrical power combiners built by the Hughes Aircraft Company of Culver City, California and patented by Robert S. Harp et al in U.S. Pat. No. 3,931,587, issued Jan. 6, 1976. However, this patented cylindrical power combiner is a narrow band, resonant cavity type of combiner, whereas the present invention to be described is directed to a wide-band non-resonant power combiner structure with improved electrical performance and certain advantages over this earlier patented combiner.
Prior attempts have been made to develop a solid state non-resonant wide-band power combiner structure, and these attempts include the proposed so-called radial line combiner. In the proposed radial line combiner, a plurality of solid state power generating devices are radially disposed around a central coaxial output line and are electrically coupled thereto for combining the output powers of these devices at a single location. One such proposed radial line combiner is disclosed by Marion E. Hines in U.S. Pat. No. 3,582,813 issued June 1, 1971 and assigned to Microwave Associates, Inc. of Burlington, Massachusetts. However, to the best of our knowledge, these prior radial line type of power combiners, including the combiner disclosed in U.S. Pat. No. 3,582,813, have never been made commercially acceptable. Furthermore, the abrupt radial-to-coaxial electrical transition in the power combiner proposed in U.S. Pat. No. 3,582,813 is not an optimum packaging configuration for accomodating impedance matching, biasing, tuning, and RF termination elements required by these types of power combiners.